Piazine antifoggants for silver halide emulsions



United States Patent 3,396,023 PIAZINE ANTIFOGGANTS FOR SILVER HALIDE EMULSIONS William W. Rees and William H. Russell, Rochester, N.Y.,

assignors to Eastman Kodak Company, Rochester, N.Y.,

a corporation of New Jersey No Drawing. Filed Aug. 24, 1965, Ser. No. 482,237 20 Claims. (CI. 96-67) ABSTRACT OF THE DISCLOSURE A photographic element comprising piazine antifoggants for silver halide emulsions and processes for developing said element are disclosed.

This invention relates to stabilizing photographic materials. In one of its aspects, this invention relates to photographic silver halide emulsions and elements containing piazines as stabilizing and antifoggin'g agents and to methods of preparing photographic materials containing such agents. In another of its aspects, this invention relates to photographic silver halide emulsions coated on polyester film base which emulsions are stabilized against fog caused by contaminants in the film base.

It is known that photographic silver halide emulsions such as gelatin silver halide emulsions, upon storage, tend to lose sensitivity and to become spontaneously developable without exposure to light. There is normally a detectable amount of the silver salt reduced during development in the area where no exposure is given; this is commonly called fog and sometimes called chemical fog where it is necessary to distinguish between it and the effects of accidental exposure to radiation. Such fog tends to increase with time and temperature in storage conditions. Furthermore, in many photographic applications it is necessary, or at least desirable, to harden a photographic silver halide emulsion layer during processing by incorporating a hard ening agent into the emulsion or a developing solution. Many of the hardening agents used for this purpose cause the photographic silver halide emulsion to fog. In addition, photographic silver halide emulsions are often coated on polyester supports which exhibit superior physical properties such as excellent dimensional stability in comparison to other supports. However, polyester supports commonly contain various side reaction products which may be formed during synthesis of the polyester as well as catalyst residue. One or all of these constituents may serve to fog photographic silver halide emulsions coated on polyester supports even though a barrier layer such as a conventional subbing layer is interposed between the support and the photographic silver halide emulsion coating.

It is evident, therefore, that the state of the photographic art will be enhanced by prowiding photographic silver halide emulsions which are stabilized against fog, particularly when coated on polyester supports and/or processed in the presence of hardening agents. Likewise, providing a means for preparing and processing such photographic silver halide emulsions and elements will represent an advance in the photographic art.

Accordingly, it is an object of this invention to provide photographic silver halide emulsions and elements which are stabilized against fog.

Another object of this invention is to provide a means for stabilizing photographic silver halide emulsions which are processed in the presence of hardening agents, particularly gelatin hardening agents.

Another object of this invention is to provide photographic elements comprising photographic silver halide emulsion layers coated on polyester film base, which emulsion layers are protected against fog caused by contaminants in the base.

Still another object of this invention is to provide photographic silver halide emulsions and elements which are stabilized against fog using a piazine.

Other objects of this invention will become apparent from an examination of the specification and claims which follow.

In accordance with this invention it has been found that fog in photographic silver halide emulsions can be substantially inhibited by the use of at least one piazine containing a pyrazine ring to which two 6-membered carbocyclic rings are fused symmetrically.

One embodiment of this invention relates to a photographic silver halide emulsion comprising a hardening agent and an antifog-gant concentration of a piazine containing a pyrazine ring to which two 6-membered carbocyclic rings are fused symmetrically.

Another embodiment of this invention relates to a photographic element comprising a support, a photographic silver halide layer and, incorporated in at least one layer of said element, a hardening agent and an antifoggant concentration of a piazine containing a pyrazine ring to which two G-membered carbocyclic rings are fused symmetrically.

Another embodiment of this invention relates to a photographic element comprising a polyester support, a photographic silver halide layer and, incorporated in at least one layer of said element an antifoggant concentration of a piazine containing a pyrazine ring to which two 6-membered carbocyclic rings are fused symmetrically.

Still another embodiment of this invention relates to developing, in the presence of a gelatin hardening agent, a photographic element comprising a support, a photographic silver halide layer and, incorporated in at least one layer of said element, an antifoggant concentration of a piazine containing a pyrazine ring to which two 6-membered carbocyclic rings are fused symmetrically.

Still another embodiment of this invention relates to developing, in a developer containing a hardening agent, a photographic element comprising a polyester support, a photographic silver halide layer, and incorporated in at least one layer of said element, an antifoggant concentration of a piazine containing a pyrazine ring to which two 6-rnembered carbocyclic rings are fused symmetrically.

Certain of the piazines employed in the practice of this invention have been used in the past as antioxidant or desensitizers in developing solution employed to develop photographic silver halide emulsion layers. However, it could not have been expected that the piazines described herein would function as useful antifoggants when incorporated into silver halide emulsion layers, particularly those processed in the presence of hardening agents or coated on polyester film base. Thus, many compounds, for example, tetraazaindene are excellent antifoggants for emulsions coated on cellulose acetate film base but they fail to substantially reduce fogging of the photographic silver halide emulsions coated on polyester film base. Also, antifoggants such as 6-nitrobenzimidazole reduce the fog of photographic silver halide emulsions coated on polyester film base but they have the disadvantage of substantially lowering the photographic speed of the silver halide emulsion. In addition, photographic elements containing piazines, as described herein, often exhibit no significant improvement in fog when processed in developer solutions containing no hardening agent, as shown in Example 3 which follows.

The piazines employed in the practice of this invention are heterocyclic compounds having two nitrogen atoms in the para position. The piazines contain a pyrazine ring to which two 6-membered carbocyclic rings are fused symmetrically and can be in the free or quaternized form. Where reference is made in the specification and claims to a piazine containing a pyrazine ring to which two 6-membered carbocyclic rings are fused symmetrically, it is intended to include the compound in its free or quaternized form. As shown in the formulas which follow, the pyrazine ring in the piazine is fused to two symmetrical carbocyclic rings which can be unsubstituted, as in phenazine, or substituted by a variety of substituents including one or more other carbocyclic rings, for example, one or two fused aromatic rings as in napthophenazine and napthazine. Examples of substituents which can be present to form the resulting substituted phenazines or napthazines include amino, hydroxy, methyl amino, ethyl amino, methyl, ethyl, dodecyl, carboxyethyl, sulfopropyl, sulf-obutyl, phenyl, benzyl, acetyl, and the like. It is obvious that the nature of the substitutents on the two 6-membered fused rings in the piazines is subject to wide variation. However, it can be seen that these piazines are characterized by a pyrazine ring to which two 6- membered carbocyclic rings are fused symmetrically.

Piazines having up to about 24 carbon atoms, preferably 12 to 20 carbon atoms, give particularly advantageous results in the practice of this invention. Piazines which are particularly useful in the practice of this invention can be represented by the following formulas:

where each of R and R is amino, hydroxy, hydrocarbyl amino, alkyl, aryl, acyloXy, acylamino or a fused 6- membered carbocyclic ring and each n is an integer of Ru I Rn X- III. I":

Z 8 I N I where each of a, b, c and d is an integer of 0 to 1 and each Z represents the non-metallic atoms necessary to form a 6-mem-bered carbocyclic ring,

where Z, a, b, c, and d are as defined above, R is alkyl, hydroxyalkyl or aryl, z is an integer of 0 to 1 and X is an anion such as halogen, chlorate, sulfate, methyl sulfate, p-toluene sulfonate "and the like. The concentration of piazine employed in the practice of this invention is subject to wide variation. In general, however, quite useful results can be obtained with concentrations in the range of about 1 to about 50, preferably about 2 to about 30 mg. per mole of silver halide. The piazines can be incorporated into the silver halide emulsion layer or some other layer, e.g., a gelatin layer which is contiguous to 2-hydroxyphenazine 2,3-dian1inophenazine 3,6-dlaminopl1enazlne gill...

3-amino-7-dimethylaminophenazlne (CH3) 2N NH:

2-metl1yl-3-amir10-7-dimethylamlnopheuazlno N f om (CHshN \N/ NH;

Naphtho-phenazine N aphtllazine Plienanthrophenazine 2,3-dihydroxyphenazine 2-acetarnino-3-acetoxyphenazine l,3-dia1nino-5-methylphenazinium chloride 1,3-diamino-o-phenylphenazinium chloride 3,7 -diamino-5-phenylphenazinium chloride 2,S-dimethyl-3,7-diamino-Bphenylphenazinium chloride 3-amin0-7-pl1enylamino-5-phenylphenazinium chloride N N Ck H 1% H2 l 2.3,7,S-phenylamino-5-phenylphenazinium chloride eHs 1,3-diamino-5-benzylphenazinium chloride I OH:

The photographic silver halides and other layers of the photographic elements can be hardened, i.e., made less soluble and more resistant to warm aqueous solutions using any of the hardening agents suitable for this purpose. Compounds which are often used in the photographic field for this purpose are hardening agents such as aldehyde hardening agents, aziridine hardening agents, hardening agents which are derivatives of dioxane, oxypolysaccharides such as oxy starch or oxy plant gums or other types of hardening agents for binding materials such as gelatin and hydrophilic colloids. It has been found that particularly good hardening agents for the practice of this invention are aldehyde hardening agents, e.g., monoaldehydes such as mucochloric acid or formaldehyde, dialdehydes, the aldehyde groups of which are separated by a linear chain of 23 carbon atoms, which chain can contain up to three substituents being alkyl and/or alkoxy of 1-4 carbon atoms, alkali soluble aldehyde-bisulfite addition compounds, particularly alkali metal bisulfite-dialdehyde addition products in which the aldehyde groups in the dialdehyde are separated by a linear chain of 2-3 carbon atoms, which chain preferably has no more than two alkyl or alkoxy substituents thereon. The bisulfite addition products release aldehyde and harden at pHs greater than 7. Suitable alkali metal bisulfites are bisulfite of alkali metals such as sodium, potassium and the like. Aldehyde-bisulfite derivatives of alkaline earth metal bisulfites, nitrogen base (ammonium, amines and the like) bisulfites and the like can also be employed.

The concentration of the hardening agent employed in the practice of this invention is subject to wide variation and will depend upon the degree of hardening desired, duration of hardening and the like. However, good results are generally obtained with concentrations in the range of about 0.1 to about 35%, preferably about 2 to about 30%, by weight, based on the total amount of vehicle employed in the layers. These hardening agents can conveniently be incorporated into the photographic silver halide emulsion layers and/or other layers, particularly gelatin containing layers of a photographic element, or they can be employed in developing compositions as is known in the art. Typical hardening agents that can be employed in the practice of this invention include formaldehyde, mucochloric acid, sodium formaldehyde bisulfite, glutaraldehyde, s-methyl glutaraldehyde, glutaraldehyde bis-sodium bisulfite, maleic dialdehyde, maleic dialdehyde bis-sodium bisulfite, methyl maleic dialdehyde, methyl succinic dialdehyde, u-methyl-a-ethoxy glutaraldehyde, a,n-butoxy glutaraldehyde, B-n-butyl glutaraldehyde, fl-isopropoxy succinic dialdehyde, butyl maleic dialdehyde and other bisulfite derivatives of dialdehydes, the aldehyde groups of which are separated by three carbon atoms and the like.

The silver halides employed in the practice of this invention include any of the photographic silver halides, as exemplified by silver bromide, silver iodide, silver chloride or mixed silver halides such as silver chlorobromide, silver bromoiodide and the like. The silver halides used can be those which form latent images predominantly on the surface of the silver halide grains or those which form latent images inside the silver halide crystals, such as those described in Davey and Knott, US. Patent 2,592,250, issued Apr. 8, 1952.

Various colloids can be used as vehicles or binding agents in the photographic emulsions and elements of this invention. Among such materials are gelatin or other colloidal materials such as colloidal albumin, cellulose derivatives, synthetic resins such as polyvinyl compounds, acrylamide polymers and the like. It is often advantageous to employ combinations of binding agents. Such combinations include, for example, mixtures of gelatin with aqueous dispersions of polymerized ethylenically unsaturated compounds, particularly polyvinyl compounds.

The photographic compositions described herein can be coated on a wide variety of supports, but preferably supports which are transparent and flexible. Typical supports include polymeric films such as cellulose acetate film, polyvinyl acetal film, polystyrene film, polypropylene film and other polyolefin film, polycarbonate film as well as glass, paper and the like. Supports such as paper which are coated with a-olefin polymers, particularly polymers of u-olefins containing 2-10 carbon atoms, as exemplified by polyethylene, polypropylene, ethylene butene polymers and the like, can also be employed. As already indicated, the piazines are particularly effective for controlling fog in photographic elements employing polyester film supports. Typical supports of this type are polyester film supports including polymers composed of bifunctional dicarboxylic acids and glycols such as polyesters prepared from 1,4-cyclohexanedimethanol and terephthalate acid. Especially useful polyester film supports are poly(alkylene terephthalates), poly(ethylene terephthalate) being particularly suitable. In the manufacture of such polyester film supports, for example, by the methods described in British Patent 578,079 or 740, 381, various side reaction products are formed which remain in the film and act as contaminants which have a tendency to cause fog when photographic silver halide emulsions are coated thereover. The use of the piazines in emulsions coated on such supports substantially inhibits fogging caused by contaminants in such polyester film supports. Preferred polyester film supports suitable for use in this invention have a thickness in the range of about 1 to about mils, preferably about 2 to about 11 mils.

The photographic silver halide emulsions described herein can be chemically sensitized with compounds of the sulfur group, noble metal salts such as gold salts, reduction sensitized with reducing agents, and combinations of these. The emulsions can also contain additional additives, particularly those known to be beneficial in photographic emulsions, including, for example, stabilizers or antifoggants, particularly the water soluble inorganic acid salts of cadmium, cobalt, manganese and zinc as disclosed in US. Patent 2,829,404, the substituted triazaindolizines as disclosed in US. Patents 2,444,605 and 2,444,607, speed increasing materials, plasticizers, a bsorbing dyes and the like. Sensitizers which gave particularly good results in the photographic compositions disclosed herein are the alkylene oxide polymers which can be employed alone or in combination with other materials, such as quaternary ammonium 'salts, as disclosed in US. Patent 2,886,437 or with mercury compounds and nitrogen containing compounds, as disclosed in US. Patent 2,751,299. The emulsions used in practicing this invention can also be X-ray or other non-spectrally sensitized emulsions as well as orthochromatic, panchromatic and infrared sensitive emulsions, particularly those sensitized with merocyanine dyes, cyanine dyes, carbocyanine dyes and the like.

This invention can be further illustrated by the following examples of preferred embodiments thereof although it will be understood that these examples are included merely for purposes of illustration and are not intended to limit the scope of the invention unless otherwise specifically indicated.

Example 1 The photographic elements described herein exhibit improved resistance to fogging when processed in the presence of a hardening agent. To illustrate, samples of a gelatin, medium-grain silver bromoiodide (98:2) photographic emulsion of the type normally used in radiography are coated on on ordinary cellulose acetate film support at coverages of 494 mg. of silver per square foot and 635 mg. of gelatin per square foot. A control sample contains no piazine while several samples contain the piazines listed in the following Table 1 at the concentrations given. The samples are given an 80 kv. direct X-ray exposure and processed for six minutes at F. in a hardening developer solution having the following composition:

Grams l-phenyl-3-pyrazolidone 1.5 Hydroquinone 25.0 Sodium sulfite, desiccated 60.0 Sodium metaborate, tetrahydrate 35.0 Tetra ammonium ethylene diamine acetate 5.0 Potassium bromide 15.0

Glutaraldehyde bis sodium bisulfite 15.0

Sodium hydroxide 2.0 Polyox WSR 301 (Union Carbide, water-soluble ethylene oxide polymer, average mol. wt. 4,000, 000) 0.01

Water to make 1 liter.

After development the samples are fixed, washed and dried in the usual manner. The fog determined on each of the samples is as follows:

TABLE 1 Piazine (mg/mol silver halide): Fog Control (0) 1.23 1,3 diamiuo 5 nethylphenazinium chloride (20) .14 1,3 diamino 5 ethylphenazinium chloride (20) .14 1,3 diamiuo 5 hydroxyethylphenazinium chloride (20) .15 1,3 diamino 5 benzylphenazinium chloride (10) .14 1,3 diamiuo 5 phenylphenazinium chloride Results similar to those reported above are obtained when the glutaraldehyde bis-sodium bisulfite is incorporated into the photographic element. In this case it is also convenient to incorporate developing agents such as 1-phenyl-3-pyrazolidone and hydroquinone into the element which can then be processed in an alkaline activator containing no developing agent.

Example 2 The procedure of Example 1 is repeated with a gelatin, medium-grain silver bromoiodide (98:2) photographic emulsion of the type normally used in radiography, but having a sensitivity which is difierent from the emulsion described in Example 1. The piazines employed and results obtained are as follows:

Example 4 The piazines described herein are particularly effective antifoggants for photographic silver halide emulsions coated on polyester film base and do not adversely affect TABLE 2 other sensitometric characteristics. To illustrate, samples Plazme Per mole sllver hahde) g of a direct X-ray type gelatine medium-grain silver broi moiodide (98:2) photographic emulsion containing the lwwyqmxyphenelme (4O) piazones listed in the following table are coated on a 2 3'dlaml nophenazme (20) p0ly(ethylene terephthalate) film base. The emulsion is Lacetammos'aCFtOXYPheHaZme (40) coated at a coverage of 1025 mg. of silver per square foot zhydroxyphenazme (40) and 1805 mg. of gelatin per square foot. For comparison From the results reported in Tables 1 and 2 it can be P p a Control Sample ing n0 PiaZ ne is also seen that the piazines described herein are effective to F0ated samples 0f the film Coatlngs when fresh, after reduce fog in photographic silver halide emulsions proclllcutlatlofl r two s at 120 F. and 15% relative essed i h presence f h d i agenm h umid1ty and after incubation for two weeks as 120 F. and 50% relative humidity are exposed for equal times Example 3 to a 250 kv. direct X-ray source and developed for six As previously indicated, the piazines described herein mlnjltes at in a developer Solution having e are very effective antifoggants for photographic silver l W1ngf0rmula: halide emulsion layers processd in the presence of hardening agents although they often exhibit no antifoggant Grams activity in the absence of such hardening agents. To illusy -p ph ol Sulfate 2.2 trate, the procedures of Examples 1 and 2 are repeated Hydr q mone 8.8 except that the samples are developed in Kodak Devel- Sodi m sulfate (anhydrous) 72.0 oper D 19b having the following composition: Sodium carbonate (anhydrous) 48,0 (37mmS Potassium bromide 4,0 N methy1-p-amin0pher101 sulfate 2.2 Water to make hter' Hydroquinone 8.8 Sodium sulfate, anhydrous 72.0 After fiXlng, Washmg and drymg 1n the usual manner, Sodium carbonate, crystanine 130.0 h p e (measu ed at a density of 0.85 above fog with Potassium bromide 2 4.0 the Il r l speed eing taken at 100 in each case), gamma Water to make 1 liter. ('y) and fog are as follows:

TABLE 4 2Wceks 120 F. 2 weeks 120 F. Piazine (mg.,lsilver mole) Fresh (15% RH) RH) Speed Fog Speed A Fog Speed x Fog Control (0 100 2. .07 105 2.70 .18 07 2.75 .14 Phenazino (4) 97 2.80 .05 105 2.75 .12 04 2. .10 2-hydroxyphenazine (16 100 2.75 .04 105 2.75 .12 91 2.80 .10 2,3-diaminophenezine 4) 95 2.75 .04 95 2.75 .11 29 2.80 .10 3-amino-2-hydroxy-pl1enazine 95 2 s0 .00 2.75 .13 95 2.80 .11 3diamino-5-methylphenazinium chloride (4) 97 2.80 .05 97 2.75 .11 91 2.80 10 3 diamino-5phenyl phenazinium chloride (4).-.. 07 2.80 .05 100 2.75 .11 91 2. 86 .10 3,7-diamiuo-5-phenylphenaziniurn chloride (8) 97 2.80 .05 102 2. s5 .12 04 2.80 .11

After development the samples are fixed, washed and dried in the usual manner. The fog determined on each of the samples is as follows:

TABLE 3 Procedure of Example 1 (Table 1) Piazine (mg./ mole silver halide): Fog Control (0) .01

1,3 diamino 5 methylphenazinium chloride (20) .02 1,3-diamino-5ethylphenaziniurn chloride (20)-- .01

1,3 diamino 5 hydroxyethylphenazinium 2,3-dihydroxyp-henazine (40) .02 2,3-diaminophenazine (20) .02 2-acetamino-3-acetoxyphenazine (40) .Ol 2-hydroxyphenazine (40) -2 .01

Thus, by the practice of this invention there is provided photographic silver halide emulsions which are stabilized against fog, particularly when these emulsions are coated on polyester supports and/or processed in the presence of hardening agents.

Although the invention has been described in considerable detail with reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected without departing from the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A photographic silver halide emulsion comprising a hardening agent and an antifoggant concentration of a piazine containing a pyrazine ring to which two 6-membered carbocyclic rings are fused symmetrically.

2. A gelatin photographic silver halide emulsion comprising a gelatin hardening agent and an antifoggant concentration of a piazine containing a pyrazine ring to which two 6-membered carbocyclic rings are fused symmetrically.

3. A gelatin photographic silver halide emulsion comprising a gelatin aldehyde hardening agent and an antifoggant concentration of a piazine having the formula:

1 1 where each of R and R is amino, hydroxy, hydrocarbyl amino, alkyl, aryl, acryloxy, acylamino or a fused 6-membered carbocyclic ring and each n is an integer of to 2.

4. A gelatin photographic silver halide emulsion comprising a gelatin aldehyde hardening agent and an antifoggant concentration of a piazine having the formula:

where each of R and R is amino, hydroxy, hydrocarbyl amino, alkyl, aryl, acyloxy, acylamino or a fused 6-membered carbocyclic ring, R is alkyl, hydroxyalkyl or aryl, X is an anion, each n is an integer of 0 to 2 and z is an integer of 0 to 1.

5. A gelatin photographic silver halide emulsion comprising glutaraldehyde bis-sodium bisulfite gelatin hardening agent and an antifoggant concentration of 1,3-diamino- S-methyl phenazinium chloride.

6. A photographic element comprising a support, a photographic silver halide layer and, incorporated in at least one layer of said element, a hardening agent and an antifoggant concentration of a piazine containing a pyrazine ring to which two 6-membered carbocyclic rings are fused symmetrically.

7. A photographic element comprising a support, a gelatin photographic silver halide layer and, incorporated in at least one layer of said element, a gelatin hardening agent and an antifoggant concentration of a piazine containing a pyrazine ring to which two 6-membered carbocyclic rings are fused symmetrically.

8. A photographic element comprising a support, a gelatin photographic silver halide layer and, incorporated in at least one layer of said element, a gelatin aldehyde hardening agent and an antifoggant concentration of a piazine having the formula:

where each of R and R' is amino, hydroxy, hydrocarbyl amino, alkyl, aryl, acyloxy, acylamino or a fused 6-membered carbocyclic ring and each n is an integer of 0 to 2.

9. A photographic element comprising a support, a gelatin photographic silver halide layer and, incorporated in at least one layer of said element, a gelatin aldehyde hardening agent and an antifoggant concentration of a piazine having the formula:

where each of R and R is amino, hydroxy, hydrocarbyl amino, alkyl, aryl, acyloxy, acylamino or a fused 6-membered carbocyclic ring, R is alkyl, hydroxyalkyl or aryl, X is an anion, each n is an integer of 0 to 2 and z is an integer of 0 to 1.

10. The photographic element of claim 8 in which the hardening agent is a dialdehyde in which the aldehyde groups are joined by a linear carbon chain of 2-3 carbon atoms.

11. The photographic element of claim 8 in which the hardening agent is an alkali soluble bisulfite-dialdehyde addition product in which the aldehyde groups are separated by a linear hydrocarbon chain of 2-3 carbon atoms.

12. A photographic element comprising a support, a gelatin photographic silver halide layer and, incorporated in at least one layer of said element, a glutaraldehyde bissodium bisulfite hardening agent and an antifoggant concentration of 1,3-diamino-5-methyl phenazinium chloride.

13. A photographic element comprising a polyester support, a photographic silver halide layer and, incorporated in at least one layer of said element an antifoggant concentration of a piazine containing a pyrazine ring to which two o-membered carbocyclic rings are fused symmetrically.

14. A photographic element comprising a polyester support, a gelatin photographic silver halide layer and, incorporated in at least one layer of said element an antifoggant concentration of a piazine containing a pyrazine ring to which two G-membered carbocyclic rings are fused symmetrically.

15. A photographic element comprising a polyester support, a gelatin photographic silver halide layer and, incorporated in at least one layer of said element, an antifoggant concentration of a piazine having the formula:

where each of R and R is amino, hydroxy, hydrocarbyl amino, alkyl, aryl, acyloxy, acylamino or a fused 6-membered carbocyclic ring and each n is an integer of 0 to 2.

16. A photographic element comprising a polyester support, a gelatin photographic silver halide layer and, incorporated in at least one layer of said element, an antifoggant concentration of a piazine having the formula:

where each of R and R is amino, hydroxy, hydrocarbyl amino, alkyl, aryl, acyloxy, acylamino or a. fused 6-membered carbocyclic ring, R is alkyl, hydroxyalkyl or aryl, X is an anion, each n is an integer of O to 2 and z is an integer of 0 to 1.

17. The photographic element of claim 13 in which the polyester support is a polyethylene terephthalate support.

18. A photographic element comprising a polyethylene terephthalate support a gelatin photographic silver halide layer and, incorporated in at least one layer of said element, an antifoggant concentration of a 1,3-diamino-5- methyl phenazinium chloride.

19. A process which comprises developing, in the presence of a gelatin hardening agent, a photographic element comprising a support, a photographic silver halide layer and, incorporated in at least one layer of said element, an antifoggant concentration of a piazine containing a pyrazine ring to which two 6-membered carbocyclic rings: are fused symmetrically.

20. A process which comprises developing, in a developer containing a hardening agent, a photographic element comprising a polyester support, a photographic silver halide layer, and incorporated in at least one layer of said element, an antifoggant concentration of a piazine containing a pyrazine ring to which two 6-membered carbocyclic rings are fused symmetrically.

References Cited UNITED STATES PATENTS 2,270,118 1/1942 Gaspar 96-53 2,410,025 10/1946 Gaspar 96--53 NORMAN G. TORCHIN, Primary Examiner.

I. R. EVERETT, Assistant Examiner. 

